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1 | =head1 NAME |
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2 | |
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3 | DBIx::Class::Manual::Cookbook - Miscellaneous recipes |
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4 | |
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5 | =head1 RECIPES |
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6 | |
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7 | =head2 Searching |
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8 | |
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9 | =head3 Paged results |
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10 | |
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11 | When you expect a large number of results, you can ask L<DBIx::Class> for a |
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12 | paged resultset, which will fetch only a defined number of records at a time: |
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13 | |
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14 | my $rs = $schema->resultset('Artist')->search( |
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15 | undef, |
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16 | { |
17 | page => 1, # page to return (defaults to 1) |
18 | rows => 10, # number of results per page |
19 | }, |
20 | ); |
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21 | |
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22 | return $rs->all(); # all records for page 1 |
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23 | |
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24 | The C<page> attribute does not have to be specified in your search: |
25 | |
26 | my $rs = $schema->resultset('Artist')->search( |
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27 | undef, |
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28 | { |
29 | rows => 10, |
30 | } |
31 | ); |
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32 | |
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33 | return $rs->page(1); # DBIx::Class::ResultSet containing first 10 records |
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34 | |
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35 | In either of the above cases, you can get a L<Data::Page> object for the |
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36 | resultset (suitable for use in e.g. a template) using the C<pager> method: |
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37 | |
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38 | return $rs->pager(); |
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39 | |
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40 | =head3 Complex WHERE clauses |
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41 | |
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42 | Sometimes you need to formulate a query using specific operators: |
43 | |
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44 | my @albums = $schema->resultset('Album')->search({ |
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45 | artist => { 'like', '%Lamb%' }, |
46 | title => { 'like', '%Fear of Fours%' }, |
47 | }); |
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48 | |
49 | This results in something like the following C<WHERE> clause: |
50 | |
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51 | WHERE artist LIKE '%Lamb%' AND title LIKE '%Fear of Fours%' |
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52 | |
53 | Other queries might require slightly more complex logic: |
54 | |
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55 | my @albums = $schema->resultset('Album')->search({ |
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56 | -or => [ |
57 | -and => [ |
58 | artist => { 'like', '%Smashing Pumpkins%' }, |
59 | title => 'Siamese Dream', |
60 | ], |
61 | artist => 'Starchildren', |
62 | ], |
63 | }); |
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64 | |
65 | This results in the following C<WHERE> clause: |
66 | |
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67 | WHERE ( artist LIKE '%Smashing Pumpkins%' AND title = 'Siamese Dream' ) |
68 | OR artist = 'Starchildren' |
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69 | |
70 | For more information on generating complex queries, see |
71 | L<SQL::Abstract/WHERE CLAUSES>. |
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72 | |
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73 | =head3 Arbitrary SQL through a custom ResultSource |
74 | |
75 | Sometimes you have to run arbitrary SQL because your query is too complex |
76 | (e.g. it contains Unions, Sub-Selects, Stored Procedures, etc.) or has to |
77 | be optimized for your database in a special way, but you still want to |
78 | get the results as a L<DBIx::Class::ResultSet>. |
79 | The recommended way to accomplish this is by defining a separate ResultSource |
80 | for your query. You can then inject complete SQL statements using a scalar |
81 | reference (this is a feature of L<SQL::Abstract>). |
82 | |
83 | Say you want to run a complex custom query on your user data, here's what |
84 | you have to add to your User class: |
85 | |
86 | package My::Schema::User; |
87 | |
88 | use base qw/DBIx::Class/; |
89 | |
90 | # ->load_components, ->table, ->add_columns, etc. |
91 | |
92 | # Make a new ResultSource based on the User class |
93 | my $source = __PACKAGE__->result_source_instance(); |
94 | my $new_source = $source->new( $source ); |
95 | $new_source->source_name( 'UserFriendsComplex' ); |
96 | |
97 | # Hand in your query as a scalar reference |
98 | # It will be added as a sub-select after FROM, |
99 | # so pay attention to the surrounding brackets! |
100 | $new_source->name( \<<SQL ); |
101 | ( SELECT u.* FROM user u |
102 | INNER JOIN user_friends f ON u.id = f.user_id |
103 | WHERE f.friend_user_id = ? |
104 | UNION |
105 | SELECT u.* FROM user u |
106 | INNER JOIN user_friends f ON u.id = f.friend_user_id |
107 | WHERE f.user_id = ? ) |
108 | SQL |
109 | |
110 | # Finally, register your new ResultSource with your Schema |
111 | My::Schema->register_source( 'UserFriendsComplex' => $new_source ); |
112 | |
113 | Next, you can execute your complex query using bind parameters like this: |
114 | |
115 | my $friends = [ $schema->resultset( 'UserFriendsComplex' )->search( {}, |
116 | { |
117 | bind => [ 12345, 12345 ] |
118 | } |
119 | ) ]; |
120 | |
121 | ... and you'll get back a perfect L<DBIx::Class::ResultSet>. |
122 | |
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123 | =head3 Using specific columns |
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124 | |
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125 | When you only want specific columns from a table, you can use |
126 | C<columns> to specify which ones you need. This is useful to avoid |
127 | loading columns with large amounts of data that you aren't about to |
128 | use anyway: |
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129 | |
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130 | my $rs = $schema->resultset('Artist')->search( |
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131 | undef, |
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132 | { |
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133 | columns => [qw/ name /] |
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134 | } |
135 | ); |
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136 | |
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137 | # Equivalent SQL: |
138 | # SELECT artist.name FROM artist |
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139 | |
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140 | This is a shortcut for C<select> and C<as>, see below. C<columns> |
141 | cannot be used together with C<select> and C<as>. |
142 | |
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143 | =head3 Using database functions or stored procedures |
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144 | |
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145 | The combination of C<select> and C<as> can be used to return the result of a |
146 | database function or stored procedure as a column value. You use C<select> to |
147 | specify the source for your column value (e.g. a column name, function, or |
148 | stored procedure name). You then use C<as> to set the column name you will use |
149 | to access the returned value: |
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150 | |
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151 | my $rs = $schema->resultset('Artist')->search( |
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152 | {}, |
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153 | { |
154 | select => [ 'name', { LENGTH => 'name' } ], |
155 | as => [qw/ name name_length /], |
156 | } |
157 | ); |
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158 | |
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159 | # Equivalent SQL: |
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160 | # SELECT name name, LENGTH( name ) |
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161 | # FROM artist |
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162 | |
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163 | Note that the C< as > attribute has absolutely nothing to with the sql |
164 | syntax C< SELECT foo AS bar > (see the documentation in |
165 | L<DBIx::Class::ResultSet/ATTRIBUTES>). If your alias exists as a |
166 | column in your base class (i.e. it was added with C<add_columns>), you |
167 | just access it as normal. Our C<Artist> class has a C<name> column, so |
168 | we just use the C<name> accessor: |
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169 | |
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170 | my $artist = $rs->first(); |
171 | my $name = $artist->name(); |
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172 | |
173 | If on the other hand the alias does not correspond to an existing column, you |
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174 | have to fetch the value using the C<get_column> accessor: |
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175 | |
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176 | my $name_length = $artist->get_column('name_length'); |
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177 | |
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178 | If you don't like using C<get_column>, you can always create an accessor for |
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179 | any of your aliases using either of these: |
180 | |
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181 | # Define accessor manually: |
182 | sub name_length { shift->get_column('name_length'); } |
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183 | |
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184 | # Or use DBIx::Class::AccessorGroup: |
185 | __PACKAGE__->mk_group_accessors('column' => 'name_length'); |
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186 | |
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187 | =head3 SELECT DISTINCT with multiple columns |
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188 | |
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189 | my $rs = $schema->resultset('Foo')->search( |
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190 | {}, |
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191 | { |
192 | select => [ |
193 | { distinct => [ $source->columns ] } |
194 | ], |
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195 | as => [ $source->columns ] # remember 'as' is not the same as SQL AS :-) |
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196 | } |
197 | ); |
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198 | |
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199 | my $count = $rs->next->get_column('count'); |
200 | |
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201 | =head3 SELECT COUNT(DISTINCT colname) |
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202 | |
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203 | my $rs = $schema->resultset('Foo')->search( |
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204 | {}, |
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205 | { |
206 | select => [ |
207 | { count => { distinct => 'colname' } } |
208 | ], |
209 | as => [ 'count' ] |
210 | } |
211 | ); |
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212 | |
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213 | =head3 Grouping results |
214 | |
215 | L<DBIx::Class> supports C<GROUP BY> as follows: |
216 | |
217 | my $rs = $schema->resultset('Artist')->search( |
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218 | {}, |
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219 | { |
220 | join => [qw/ cds /], |
221 | select => [ 'name', { count => 'cds.cdid' } ], |
222 | as => [qw/ name cd_count /], |
223 | group_by => [qw/ name /] |
224 | } |
225 | ); |
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226 | |
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227 | # Equivalent SQL: |
228 | # SELECT name, COUNT( cds.cdid ) FROM artist me |
229 | # LEFT JOIN cd cds ON ( cds.artist = me.artistid ) |
230 | # GROUP BY name |
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231 | |
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232 | Please see L<DBIx::Class::ResultSet/ATTRIBUTES> documentation if you |
233 | are in any way unsure about the use of the attributes above (C< join |
234 | >, C< select >, C< as > and C< group_by >). |
235 | |
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236 | =head3 Predefined searches |
237 | |
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238 | You can write your own L<DBIx::Class::ResultSet> class by inheriting from it |
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239 | and define often used searches as methods: |
240 | |
241 | package My::DBIC::ResultSet::CD; |
242 | use strict; |
243 | use warnings; |
244 | use base 'DBIx::Class::ResultSet'; |
245 | |
246 | sub search_cds_ordered { |
247 | my ($self) = @_; |
248 | |
249 | return $self->search( |
250 | {}, |
251 | { order_by => 'name DESC' }, |
252 | ); |
253 | } |
254 | |
255 | 1; |
256 | |
257 | To use your resultset, first tell DBIx::Class to create an instance of it |
258 | for you, in your My::DBIC::Schema::CD class: |
259 | |
260 | __PACKAGE__->resultset_class('My::DBIC::ResultSet::CD'); |
261 | |
262 | Then call your new method in your code: |
263 | |
264 | my $ordered_cds = $schema->resultset('CD')->search_cds_ordered(); |
265 | |
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266 | =head3 Using SQL functions on the left hand side of a comparison |
267 | |
268 | Using SQL functions on the left hand side of a comparison is generally |
269 | not a good idea since it requires a scan of the entire table. However, |
270 | it can be accomplished with C<DBIx::Class> when necessary. |
271 | |
272 | If you do not have quoting on, simply include the function in your search |
273 | specification as you would any column: |
274 | |
275 | $rs->search({ 'YEAR(date_of_birth)' => 1979 }); |
276 | |
277 | With quoting on, or for a more portable solution, use the C<where> |
278 | attribute: |
279 | |
280 | $rs->search({}, { where => \'YEAR(date_of_birth) = 1979' }); |
281 | |
282 | =begin hidden |
283 | |
284 | (When the bind args ordering bug is fixed, this technique will be better |
285 | and can replace the one above.) |
286 | |
287 | With quoting on, or for a more portable solution, use the C<where> and |
288 | C<bind> attributes: |
289 | |
290 | $rs->search({}, { |
291 | where => \'YEAR(date_of_birth) = ?', |
292 | bind => [ 1979 ] |
293 | }); |
294 | |
295 | =end hidden |
296 | |
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297 | =head2 Using joins and prefetch |
298 | |
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299 | You can use the C<join> attribute to allow searching on, or sorting your |
300 | results by, one or more columns in a related table. To return all CDs matching |
301 | a particular artist name: |
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302 | |
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303 | my $rs = $schema->resultset('CD')->search( |
304 | { |
305 | 'artist.name' => 'Bob Marley' |
306 | }, |
307 | { |
308 | join => [qw/artist/], # join the artist table |
309 | } |
310 | ); |
311 | |
312 | # Equivalent SQL: |
313 | # SELECT cd.* FROM cd |
314 | # JOIN artist ON cd.artist = artist.id |
315 | # WHERE artist.name = 'Bob Marley' |
316 | |
317 | If required, you can now sort on any column in the related tables by including |
318 | it in your C<order_by> attribute: |
319 | |
320 | my $rs = $schema->resultset('CD')->search( |
321 | { |
322 | 'artist.name' => 'Bob Marley' |
323 | }, |
324 | { |
325 | join => [qw/ artist /], |
326 | order_by => [qw/ artist.name /] |
327 | } |
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328 | ); |
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329 | |
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330 | # Equivalent SQL: |
331 | # SELECT cd.* FROM cd |
332 | # JOIN artist ON cd.artist = artist.id |
333 | # WHERE artist.name = 'Bob Marley' |
334 | # ORDER BY artist.name |
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335 | |
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336 | Note that the C<join> attribute should only be used when you need to search or |
337 | sort using columns in a related table. Joining related tables when you only |
338 | need columns from the main table will make performance worse! |
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339 | |
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340 | Now let's say you want to display a list of CDs, each with the name of the |
341 | artist. The following will work fine: |
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342 | |
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343 | while (my $cd = $rs->next) { |
344 | print "CD: " . $cd->title . ", Artist: " . $cd->artist->name; |
345 | } |
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346 | |
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347 | There is a problem however. We have searched both the C<cd> and C<artist> tables |
348 | in our main query, but we have only returned data from the C<cd> table. To get |
349 | the artist name for any of the CD objects returned, L<DBIx::Class> will go back |
350 | to the database: |
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351 | |
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352 | SELECT artist.* FROM artist WHERE artist.id = ? |
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353 | |
354 | A statement like the one above will run for each and every CD returned by our |
355 | main query. Five CDs, five extra queries. A hundred CDs, one hundred extra |
356 | queries! |
357 | |
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358 | Thankfully, L<DBIx::Class> has a C<prefetch> attribute to solve this problem. |
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359 | This allows you to fetch results from related tables in advance: |
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360 | |
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361 | my $rs = $schema->resultset('CD')->search( |
362 | { |
363 | 'artist.name' => 'Bob Marley' |
364 | }, |
365 | { |
366 | join => [qw/ artist /], |
367 | order_by => [qw/ artist.name /], |
368 | prefetch => [qw/ artist /] # return artist data too! |
369 | } |
370 | ); |
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371 | |
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372 | # Equivalent SQL (note SELECT from both "cd" and "artist"): |
373 | # SELECT cd.*, artist.* FROM cd |
374 | # JOIN artist ON cd.artist = artist.id |
375 | # WHERE artist.name = 'Bob Marley' |
376 | # ORDER BY artist.name |
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377 | |
378 | The code to print the CD list remains the same: |
379 | |
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380 | while (my $cd = $rs->next) { |
381 | print "CD: " . $cd->title . ", Artist: " . $cd->artist->name; |
382 | } |
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383 | |
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384 | L<DBIx::Class> has now prefetched all matching data from the C<artist> table, |
ea6309e2 |
385 | so no additional SQL statements are executed. You now have a much more |
386 | efficient query. |
387 | |
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388 | Note that as of L<DBIx::Class> 0.05999_01, C<prefetch> I<can> be used with |
389 | C<has_many> relationships. |
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390 | |
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391 | Also note that C<prefetch> should only be used when you know you will |
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392 | definitely use data from a related table. Pre-fetching related tables when you |
393 | only need columns from the main table will make performance worse! |
394 | |
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395 | =head3 Multi-step joins |
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396 | |
397 | Sometimes you want to join more than one relationship deep. In this example, |
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398 | we want to find all C<Artist> objects who have C<CD>s whose C<LinerNotes> |
399 | contain a specific string: |
400 | |
401 | # Relationships defined elsewhere: |
402 | # Artist->has_many('cds' => 'CD', 'artist'); |
403 | # CD->has_one('liner_notes' => 'LinerNotes', 'cd'); |
404 | |
405 | my $rs = $schema->resultset('Artist')->search( |
406 | { |
407 | 'liner_notes.notes' => { 'like', '%some text%' }, |
408 | }, |
409 | { |
410 | join => { |
411 | 'cds' => 'liner_notes' |
412 | } |
413 | } |
414 | ); |
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415 | |
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416 | # Equivalent SQL: |
417 | # SELECT artist.* FROM artist |
418 | # JOIN ( cd ON artist.id = cd.artist ) |
419 | # JOIN ( liner_notes ON cd.id = liner_notes.cd ) |
420 | # WHERE liner_notes.notes LIKE '%some text%' |
ea6309e2 |
421 | |
422 | Joins can be nested to an arbitrary level. So if we decide later that we |
423 | want to reduce the number of Artists returned based on who wrote the liner |
424 | notes: |
425 | |
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426 | # Relationship defined elsewhere: |
427 | # LinerNotes->belongs_to('author' => 'Person'); |
428 | |
429 | my $rs = $schema->resultset('Artist')->search( |
430 | { |
431 | 'liner_notes.notes' => { 'like', '%some text%' }, |
432 | 'author.name' => 'A. Writer' |
433 | }, |
434 | { |
435 | join => { |
436 | 'cds' => { |
437 | 'liner_notes' => 'author' |
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438 | } |
bade79c4 |
439 | } |
440 | } |
441 | ); |
ea6309e2 |
442 | |
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443 | # Equivalent SQL: |
444 | # SELECT artist.* FROM artist |
445 | # JOIN ( cd ON artist.id = cd.artist ) |
446 | # JOIN ( liner_notes ON cd.id = liner_notes.cd ) |
447 | # JOIN ( author ON author.id = liner_notes.author ) |
448 | # WHERE liner_notes.notes LIKE '%some text%' |
449 | # AND author.name = 'A. Writer' |
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450 | |
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451 | =head2 Multi-step prefetch |
452 | |
453 | From 0.04999_05 onwards, C<prefetch> can be nested more than one relationship |
454 | deep using the same syntax as a multi-step join: |
455 | |
456 | my $rs = $schema->resultset('Tag')->search( |
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457 | {}, |
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458 | { |
459 | prefetch => { |
460 | cd => 'artist' |
461 | } |
462 | } |
463 | ); |
464 | |
465 | # Equivalent SQL: |
466 | # SELECT tag.*, cd.*, artist.* FROM tag |
467 | # JOIN cd ON tag.cd = cd.cdid |
468 | # JOIN artist ON cd.artist = artist.artistid |
469 | |
470 | Now accessing our C<cd> and C<artist> relationships does not need additional |
471 | SQL statements: |
472 | |
473 | my $tag = $rs->first; |
474 | print $tag->cd->artist->name; |
475 | |
ac2803ef |
476 | =head2 Columns of data |
477 | |
478 | If you want to find the sum of a particular column there are several |
479 | ways, the obvious one is to use search: |
480 | |
481 | my $rs = $schema->resultset('Items')->search( |
482 | {}, |
483 | { |
484 | select => [ { sum => 'Cost' } ], |
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485 | as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL |
ac2803ef |
486 | } |
487 | ); |
488 | my $tc = $rs->first->get_column('total_cost'); |
489 | |
490 | Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets |
491 | returned when you ask the C<ResultSet> for a column using |
492 | C<get_column>: |
493 | |
494 | my $cost = $schema->resultset('Items')->get_column('Cost'); |
495 | my $tc = $cost->sum; |
496 | |
497 | With this you can also do: |
498 | |
499 | my $minvalue = $cost->min; |
500 | my $maxvalue = $cost->max; |
501 | |
502 | Or just iterate through the values of this column only: |
503 | |
504 | while ( my $c = $cost->next ) { |
505 | print $c; |
506 | } |
507 | |
508 | foreach my $c ($cost->all) { |
509 | print $c; |
510 | } |
511 | |
709353af |
512 | C<ResultSetColumn> only has a limited number of built-in functions, if |
513 | you need one that it doesn't have, then you can use the C<func> method |
514 | instead: |
515 | |
516 | my $avg = $cost->func('AVERAGE'); |
517 | |
518 | This will cause the following SQL statement to be run: |
519 | |
520 | SELECT AVERAGE(Cost) FROM Items me |
521 | |
522 | Which will of course only work if your database supports this function. |
ac2803ef |
523 | See L<DBIx::Class::ResultSetColumn> for more documentation. |
524 | |
acee4e4d |
525 | =head2 Using relationships |
526 | |
527 | =head3 Create a new row in a related table |
528 | |
529 | my $book->create_related('author', { name => 'Fred'}); |
530 | |
531 | =head3 Search in a related table |
532 | |
533 | Only searches for books named 'Titanic' by the author in $author. |
534 | |
535 | my $author->search_related('books', { name => 'Titanic' }); |
536 | |
537 | =head3 Delete data in a related table |
538 | |
539 | Deletes only the book named Titanic by the author in $author. |
540 | |
541 | my $author->delete_related('books', { name => 'Titanic' }); |
542 | |
f8bad769 |
543 | =head3 Ordering a relationship result set |
544 | |
545 | If you always want a relation to be ordered, you can specify this when you |
546 | create the relationship. |
547 | |
548 | To order C<< $book->pages >> by descending page_number. |
549 | |
550 | Book->has_many('pages' => 'Page', 'book', { order_by => \'page_number DESC'} ); |
551 | |
552 | |
553 | |
87980de7 |
554 | =head2 Transactions |
555 | |
556 | As of version 0.04001, there is improved transaction support in |
85f78622 |
557 | L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an |
181a28f4 |
558 | example of the recommended way to use it: |
87980de7 |
559 | |
181a28f4 |
560 | my $genus = $schema->resultset('Genus')->find(12); |
561 | |
70634260 |
562 | my $coderef2 = sub { |
563 | $genus->extinct(1); |
564 | $genus->update; |
565 | }; |
566 | |
181a28f4 |
567 | my $coderef1 = sub { |
35d4fe78 |
568 | $genus->add_to_species({ name => 'troglodyte' }); |
569 | $genus->wings(2); |
570 | $genus->update; |
70634260 |
571 | $schema->txn_do($coderef2); # Can have a nested transaction |
181a28f4 |
572 | return $genus->species; |
573 | }; |
574 | |
181a28f4 |
575 | my $rs; |
576 | eval { |
70634260 |
577 | $rs = $schema->txn_do($coderef1); |
181a28f4 |
578 | }; |
579 | |
580 | if ($@) { # Transaction failed |
581 | die "the sky is falling!" # |
582 | if ($@ =~ /Rollback failed/); # Rollback failed |
583 | |
584 | deal_with_failed_transaction(); |
35d4fe78 |
585 | } |
87980de7 |
586 | |
181a28f4 |
587 | Nested transactions will work as expected. That is, only the outermost |
588 | transaction will actually issue a commit to the $dbh, and a rollback |
589 | at any level of any transaction will cause the entire nested |
590 | transaction to fail. Support for savepoints and for true nested |
40dbc108 |
591 | transactions (for databases that support them) will hopefully be added |
592 | in the future. |
ee38fa40 |
593 | |
130c6439 |
594 | =head2 Many-to-many relationships |
ee38fa40 |
595 | |
787d6a29 |
596 | This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>: |
ea6309e2 |
597 | |
bade79c4 |
598 | package My::DB; |
599 | # ... set up connection ... |
600 | |
601 | package My::User; |
602 | use base 'My::DB'; |
603 | __PACKAGE__->table('user'); |
604 | __PACKAGE__->add_columns(qw/id name/); |
605 | __PACKAGE__->set_primary_key('id'); |
606 | __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user'); |
607 | __PACKAGE__->many_to_many('addresses' => 'user_address', 'address'); |
608 | |
609 | package My::UserAddress; |
610 | use base 'My::DB'; |
611 | __PACKAGE__->table('user_address'); |
612 | __PACKAGE__->add_columns(qw/user address/); |
613 | __PACKAGE__->set_primary_key(qw/user address/); |
614 | __PACKAGE__->belongs_to('user' => 'My::User'); |
615 | __PACKAGE__->belongs_to('address' => 'My::Address'); |
616 | |
617 | package My::Address; |
618 | use base 'My::DB'; |
619 | __PACKAGE__->table('address'); |
620 | __PACKAGE__->add_columns(qw/id street town area_code country/); |
621 | __PACKAGE__->set_primary_key('id'); |
622 | __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address'); |
623 | __PACKAGE__->many_to_many('users' => 'user_address', 'user'); |
624 | |
625 | $rs = $user->addresses(); # get all addresses for a user |
626 | $rs = $address->users(); # get all users for an address |
627 | |
628 | =head2 Setting default values for a row |
a00e1684 |
629 | |
35d4fe78 |
630 | It's as simple as overriding the C<new> method. Note the use of |
40dbc108 |
631 | C<next::method>. |
a00e1684 |
632 | |
35d4fe78 |
633 | sub new { |
634 | my ( $class, $attrs ) = @_; |
40dbc108 |
635 | |
35d4fe78 |
636 | $attrs->{foo} = 'bar' unless defined $attrs->{foo}; |
40dbc108 |
637 | |
df65edd2 |
638 | my $new = $class->next::method($attrs); |
8b50216e |
639 | |
df65edd2 |
640 | return $new; |
35d4fe78 |
641 | } |
a00e1684 |
642 | |
4a3c6354 |
643 | For more information about C<next::method>, look in the L<Class::C3> |
644 | documentation. See also L<DBIx::Class::Manual::Component> for more |
645 | ways to write your own base classes to do this. |
646 | |
647 | People looking for ways to do "triggers" with DBIx::Class are probably |
ab872312 |
648 | just looking for this. |
4a3c6354 |
649 | |
25af00d7 |
650 | =head2 Stringification |
651 | |
40dbc108 |
652 | Employ the standard stringification technique by using the C<overload> |
462bb847 |
653 | module. |
654 | |
655 | To make an object stringify itself as a single column, use something |
656 | like this (replace C<foo> with the column/method of your choice): |
25af00d7 |
657 | |
0472cc04 |
658 | use overload '""' => sub { shift->name}, fallback => 1; |
25af00d7 |
659 | |
462bb847 |
660 | For more complex stringification, you can use an anonymous subroutine: |
661 | |
662 | use overload '""' => sub { $_[0]->name . ", " . |
663 | $_[0]->address }, fallback => 1; |
664 | |
324572ca |
665 | =head3 Stringification Example |
462bb847 |
666 | |
667 | Suppose we have two tables: C<Product> and C<Category>. The table |
668 | specifications are: |
669 | |
670 | Product(id, Description, category) |
671 | Category(id, Description) |
672 | |
673 | C<category> is a foreign key into the Category table. |
674 | |
675 | If you have a Product object C<$obj> and write something like |
676 | |
677 | print $obj->category |
678 | |
679 | things will not work as expected. |
680 | |
681 | To obtain, for example, the category description, you should add this |
682 | method to the class defining the Category table: |
683 | |
684 | use overload "" => sub { |
685 | my $self = shift; |
686 | |
687 | return $self->Description; |
77713550 |
688 | }, fallback => 1; |
462bb847 |
689 | |
bade79c4 |
690 | =head2 Disconnecting cleanly |
691 | |
692 | If you find yourself quitting an app with Control-C a lot during |
693 | development, you might like to put the following signal handler in |
694 | your main database class to make sure it disconnects cleanly: |
695 | |
696 | $SIG{INT} = sub { |
6d1bf0a9 |
697 | __PACKAGE__->storage->disconnect; |
bade79c4 |
698 | }; |
699 | |
362500af |
700 | =head2 Schema import/export |
701 | |
264f1571 |
702 | To create a DBIx::Class schema from an existing database, use |
703 | L<DBIx::Class::Schema::Loader>'s C<make_schema_at>: |
362500af |
704 | |
264f1571 |
705 | perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])' |
362500af |
706 | |
264f1571 |
707 | The following functionality requires you to have L<SQL::Translator> |
708 | (also known as "SQL Fairy") installed. |
362500af |
709 | |
264f1571 |
710 | To create a set of database-specific .sql files for the above schema: |
362500af |
711 | |
264f1571 |
712 | my $schema = My::Schema->connect($dsn); |
713 | $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'], |
714 | '0.1', |
715 | '/dbscriptdir/' |
716 | ); |
717 | |
718 | By default this will create schema files in the current directory, for |
719 | MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm. |
720 | |
721 | To create a new database using the schema: |
722 | |
723 | my $schema = My::Schema->connect($dsn); |
724 | $schema->deploy({ add_drop_tables => 1}); |
725 | |
726 | To import created .sql files using the mysql client: |
727 | |
728 | mysql -h "host" -D "database" -u "user" -p < My_Schema_1.0_MySQL.sql |
729 | |
730 | To create C<ALTER TABLE> conversion scripts to update a database to a |
731 | newer version of your schema at a later point, first set a new |
732 | $VERSION in your Schema file, then: |
733 | |
734 | my $schema = My::Schema->connect($dsn); |
735 | $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'], |
736 | '0.2', |
737 | '/dbscriptdir/', |
738 | '0.1' |
739 | ); |
740 | |
741 | This will produce new database-specific .sql files for the new version |
742 | of the schema, plus scripts to convert from version 0.1 to 0.2. This |
743 | requires that the files for 0.1 as created above are available in the |
744 | given directory to diff against. |
362500af |
745 | |
362500af |
746 | |
b0a20454 |
747 | =head2 Easy migration from class-based to schema-based setup |
748 | |
749 | You want to start using the schema-based approach to L<DBIx::Class> |
750 | (see L<SchemaIntro.pod>), but have an established class-based setup with lots |
751 | of existing classes that you don't want to move by hand. Try this nifty script |
752 | instead: |
753 | |
754 | use MyDB; |
755 | use SQL::Translator; |
756 | |
757 | my $schema = MyDB->schema_instance; |
758 | |
759 | my $translator = SQL::Translator->new( |
760 | debug => $debug || 0, |
761 | trace => $trace || 0, |
762 | no_comments => $no_comments || 0, |
763 | show_warnings => $show_warnings || 0, |
764 | add_drop_table => $add_drop_table || 0, |
765 | validate => $validate || 0, |
766 | parser_args => { |
767 | 'DBIx::Schema' => $schema, |
c5f36986 |
768 | }, |
b0a20454 |
769 | producer_args => { |
770 | 'prefix' => 'My::Schema', |
c5f36986 |
771 | }, |
b0a20454 |
772 | ); |
773 | |
d240abac |
774 | $translator->parser('SQL::Translator::Parser::DBIx::Class'); |
775 | $translator->producer('SQL::Translator::Producer::DBIx::Class::File'); |
b0a20454 |
776 | |
777 | my $output = $translator->translate(@args) or die |
778 | "Error: " . $translator->error; |
779 | |
780 | print $output; |
781 | |
782 | You could use L<Module::Find> to search for all subclasses in the MyDB::* |
880a1a0c |
783 | namespace, which is currently left as an exercise for the reader. |
b0a20454 |
784 | |
362500af |
785 | =head2 Schema versioning |
786 | |
787 | The following example shows simplistically how you might use DBIx::Class to |
788 | deploy versioned schemas to your customers. The basic process is as follows: |
789 | |
da4779ad |
790 | =over 4 |
791 | |
792 | =item 1. |
793 | |
794 | Create a DBIx::Class schema |
795 | |
796 | =item 2. |
797 | |
798 | Save the schema |
799 | |
800 | =item 3. |
801 | |
802 | Deploy to customers |
803 | |
804 | =item 4. |
805 | |
806 | Modify schema to change functionality |
807 | |
808 | =item 5. |
809 | |
810 | Deploy update to customers |
811 | |
812 | =back |
362500af |
813 | |
814 | =head3 Create a DBIx::Class schema |
815 | |
816 | This can either be done manually, or generated from an existing database as |
817 | described under C<Schema import/export>. |
818 | |
819 | =head3 Save the schema |
820 | |
264f1571 |
821 | Call L<DBIx::Class::Schema/create_ddl_dir> as above under L<Schema |
822 | import/export>. |
362500af |
823 | |
824 | =head3 Deploy to customers |
825 | |
826 | There are several ways you could deploy your schema. These are probably |
827 | beyond the scope of this recipe, but might include: |
828 | |
da4779ad |
829 | =over 4 |
830 | |
831 | =item 1. |
832 | |
833 | Require customer to apply manually using their RDBMS. |
834 | |
835 | =item 2. |
836 | |
837 | Package along with your app, making database dump/schema update/tests |
362500af |
838 | all part of your install. |
839 | |
da4779ad |
840 | =back |
841 | |
362500af |
842 | =head3 Modify the schema to change functionality |
843 | |
264f1571 |
844 | As your application evolves, it may be necessary to modify your schema |
845 | to change functionality. Once the changes are made to your schema in |
846 | DBIx::Class, export the modified schema and the conversion scripts as |
847 | in L<Schema import/export>. |
362500af |
848 | |
849 | =head3 Deploy update to customers |
850 | |
264f1571 |
851 | Add the L<DBIx::Class::Schema::Versioned> schema component to your |
852 | Schema class. This will add a new table to your database called |
853 | C<SchemaVersions> which will keep track of which version is installed |
854 | and warn if the user trys to run a newer schema version than the |
855 | database thinks it has. |
856 | |
857 | Alternatively, you can send the conversion sql scripts to your |
858 | customers as above. |
362500af |
859 | |
7be93b07 |
860 | =head2 Setting limit dialect for SQL::Abstract::Limit |
861 | |
324572ca |
862 | In some cases, SQL::Abstract::Limit cannot determine the dialect of |
863 | the remote SQL server by looking at the database handle. This is a |
864 | common problem when using the DBD::JDBC, since the DBD-driver only |
865 | know that in has a Java-driver available, not which JDBC driver the |
866 | Java component has loaded. This specifically sets the limit_dialect |
867 | to Microsoft SQL-server (See more names in SQL::Abstract::Limit |
868 | -documentation. |
7be93b07 |
869 | |
870 | __PACKAGE__->storage->sql_maker->limit_dialect('mssql'); |
871 | |
324572ca |
872 | The JDBC bridge is one way of getting access to a MSSQL server from a platform |
7be93b07 |
873 | that Microsoft doesn't deliver native client libraries for. (e.g. Linux) |
874 | |
324572ca |
875 | =head2 Setting quoting for the generated SQL. |
2437a1e3 |
876 | |
324572ca |
877 | If the database contains column names with spaces and/or reserved words, they |
878 | need to be quoted in the SQL queries. This is done using: |
2437a1e3 |
879 | |
880 | __PACKAGE__->storage->sql_maker->quote_char([ qw/[ ]/] ); |
881 | __PACKAGE__->storage->sql_maker->name_sep('.'); |
882 | |
324572ca |
883 | The first sets the quote characters. Either a pair of matching |
884 | brackets, or a C<"> or C<'>: |
2437a1e3 |
885 | |
886 | __PACKAGE__->storage->sql_maker->quote_char('"'); |
887 | |
324572ca |
888 | Check the documentation of your database for the correct quote |
889 | characters to use. C<name_sep> needs to be set to allow the SQL |
890 | generator to put the quotes the correct place. |
2437a1e3 |
891 | |
086b93a2 |
892 | =head2 Overloading methods |
893 | |
ab872312 |
894 | L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of |
895 | method calls, useful for things like default values and triggers. You have to |
896 | use calls to C<next::method> to overload methods. More information on using |
897 | L<Class::C3> with L<DBIx::Class> can be found in |
086b93a2 |
898 | L<DBIx::Class::Manual::Component>. |
899 | |
900 | =head3 Changing one field whenever another changes |
901 | |
902 | For example, say that you have three columns, C<id>, C<number>, and |
903 | C<squared>. You would like to make changes to C<number> and have |
904 | C<squared> be automagically set to the value of C<number> squared. |
905 | You can accomplish this by overriding C<store_column>: |
906 | |
907 | sub store_column { |
908 | my ( $self, $name, $value ) = @_; |
909 | if ($name eq 'number') { |
910 | $self->squared($value * $value); |
911 | } |
912 | $self->next::method($name, $value); |
913 | } |
914 | |
915 | Note that the hard work is done by the call to C<next::method>, which |
324572ca |
916 | redispatches your call to store_column in the superclass(es). |
086b93a2 |
917 | |
918 | =head3 Automatically creating related objects |
919 | |
324572ca |
920 | You might have a class C<Artist> which has many C<CD>s. Further, if you |
086b93a2 |
921 | want to create a C<CD> object every time you insert an C<Artist> object. |
ccbebdbc |
922 | You can accomplish this by overriding C<insert> on your objects: |
086b93a2 |
923 | |
924 | sub insert { |
ccbebdbc |
925 | my ( $self, @args ) = @_; |
926 | $self->next::method(@args); |
086b93a2 |
927 | $self->cds->new({})->fill_from_artist($self)->insert; |
928 | return $self; |
929 | } |
930 | |
931 | where C<fill_from_artist> is a method you specify in C<CD> which sets |
932 | values in C<CD> based on the data in the C<Artist> object you pass in. |
933 | |
1def3451 |
934 | =head2 Debugging DBIx::Class objects with Data::Dumper |
935 | |
936 | L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can |
937 | be hard to find the pertinent data in all the data it can generate. |
938 | Specifically, if one naively tries to use it like so, |
939 | |
940 | use Data::Dumper; |
941 | |
942 | my $cd = $schema->resultset('CD')->find(1); |
943 | print Dumper($cd); |
944 | |
945 | several pages worth of data from the CD object's schema and result source will |
946 | be dumped to the screen. Since usually one is only interested in a few column |
947 | values of the object, this is not very helpful. |
948 | |
949 | Luckily, it is possible to modify the data before L<Data::Dumper> outputs |
950 | it. Simply define a hook that L<Data::Dumper> will call on the object before |
951 | dumping it. For example, |
952 | |
953 | package My::DB::CD; |
954 | |
955 | sub _dumper_hook { |
99fb1058 |
956 | $_[0] = bless { |
957 | %{ $_[0] }, |
1def3451 |
958 | result_source => undef, |
99fb1058 |
959 | }, ref($_[0]); |
1def3451 |
960 | } |
961 | |
962 | [...] |
963 | |
964 | use Data::Dumper; |
965 | |
22139027 |
966 | local $Data::Dumper::Freezer = '_dumper_hook'; |
1def3451 |
967 | |
968 | my $cd = $schema->resultset('CD')->find(1); |
969 | print Dumper($cd); |
970 | # dumps $cd without its ResultSource |
971 | |
972 | If the structure of your schema is such that there is a common base class for |
973 | all your table classes, simply put a method similar to C<_dumper_hook> in the |
974 | base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper> |
975 | will automagically clean up your data before printing it. See |
976 | L<Data::Dumper/EXAMPLES> for more information. |
977 | |
1def3451 |
978 | =head2 Retrieving a row object's Schema |
979 | |
324572ca |
980 | It is possible to get a Schema object from a row object like so: |
1def3451 |
981 | |
982 | my $schema = $cd->result_source->schema; |
324572ca |
983 | # use the schema as normal: |
984 | my $artist_rs = $schema->resultset('Artist'); |
1def3451 |
985 | |
986 | This can be useful when you don't want to pass around a Schema object to every |
987 | method. |
988 | |
4c248161 |
989 | =head2 Profiling |
990 | |
85f78622 |
991 | When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL |
4c248161 |
992 | executed as well as notifications of query completion and transaction |
993 | begin/commit. If you'd like to profile the SQL you can subclass the |
994 | L<DBIx::Class::Storage::Statistics> class and write your own profiling |
995 | mechanism: |
996 | |
997 | package My::Profiler; |
998 | use strict; |
999 | |
1000 | use base 'DBIx::Class::Storage::Statistics'; |
1001 | |
1002 | use Time::HiRes qw(time); |
1003 | |
1004 | my $start; |
1005 | |
1006 | sub query_start { |
1007 | my $self = shift(); |
1008 | my $sql = shift(); |
1009 | my $params = @_; |
1010 | |
70f39278 |
1011 | $self->print("Executing $sql: ".join(', ', @params)."\n"); |
4c248161 |
1012 | $start = time(); |
1013 | } |
1014 | |
1015 | sub query_end { |
1016 | my $self = shift(); |
1017 | my $sql = shift(); |
1018 | my @params = @_; |
1019 | |
70f39278 |
1020 | my $elapsed = sprintf("%0.4f", time() - $start); |
1021 | $self->print("Execution took $elapsed seconds.\n"); |
4c248161 |
1022 | $start = undef; |
1023 | } |
1024 | |
1025 | 1; |
1026 | |
1027 | You can then install that class as the debugging object: |
1028 | |
70f39278 |
1029 | __PACKAGE__->storage->debugobj(new My::Profiler()); |
1030 | __PACKAGE__->storage->debug(1); |
4c248161 |
1031 | |
1032 | A more complicated example might involve storing each execution of SQL in an |
1033 | array: |
1034 | |
1035 | sub query_end { |
1036 | my $self = shift(); |
1037 | my $sql = shift(); |
1038 | my @params = @_; |
1039 | |
1040 | my $elapsed = time() - $start; |
1041 | push(@{ $calls{$sql} }, { |
1042 | params => \@params, |
1043 | elapsed => $elapsed |
1044 | }); |
1045 | } |
1046 | |
1047 | You could then create average, high and low execution times for an SQL |
1048 | statement and dig down to see if certain parameters cause aberrant behavior. |
70f39278 |
1049 | You might want to check out L<DBIx::Class::QueryLog> as well. |
4c248161 |
1050 | |
e8e9e5c7 |
1051 | =head2 Getting the value of the primary key for the last database insert |
1052 | |
74413b83 |
1053 | AKA getting last_insert_id |
1054 | |
e8e9e5c7 |
1055 | If you are using PK::Auto, this is straightforward: |
1056 | |
74413b83 |
1057 | my $foo = $rs->create(\%blah); |
e8e9e5c7 |
1058 | # do more stuff |
1059 | my $id = $foo->id; # foo->my_primary_key_field will also work. |
1060 | |
1061 | If you are not using autoincrementing primary keys, this will probably |
1062 | not work, but then you already know the value of the last primary key anyway. |
1063 | |
824f4422 |
1064 | =head2 Dynamic Sub-classing DBIx::Class proxy classes |
1065 | (AKA multi-class object inflation from one table) |
1066 | |
324572ca |
1067 | L<DBIx::Class> classes are proxy classes, therefore some different |
1068 | techniques need to be employed for more than basic subclassing. In |
1069 | this example we have a single user table that carries a boolean bit |
1070 | for admin. We would like like to give the admin users |
1071 | objects(L<DBIx::Class::Row>) the same methods as a regular user but |
1072 | also special admin only methods. It doesn't make sense to create two |
1073 | seperate proxy-class files for this. We would be copying all the user |
1074 | methods into the Admin class. There is a cleaner way to accomplish |
1075 | this. |
1076 | |
c6d147b6 |
1077 | Overriding the C<inflate_result> method within the User proxy-class |
324572ca |
1078 | gives us the effect we want. This method is called by |
1079 | L<DBIx::Class::ResultSet> when inflating a result from storage. So we |
1080 | grab the object being returned, inspect the values we are looking for, |
1081 | bless it if it's an admin object, and then return it. See the example |
1082 | below: |
824f4422 |
1083 | |
1084 | B<Schema Definition> |
1085 | |
1086 | package DB::Schema; |
1087 | |
1088 | use base qw/DBIx::Class::Schema/; |
1089 | |
1090 | __PACKAGE__->load_classes(qw/User/); |
1091 | |
1092 | |
1093 | B<Proxy-Class definitions> |
1094 | |
1095 | package DB::Schema::User; |
1096 | |
1097 | use strict; |
1098 | use warnings; |
1099 | use base qw/DBIx::Class/; |
1100 | |
1101 | ### Defined what our admin class is for ensure_class_loaded |
1102 | my $admin_class = __PACKAGE__ . '::Admin'; |
1103 | |
324572ca |
1104 | __PACKAGE__->load_components(qw/Core/); |
824f4422 |
1105 | |
1106 | __PACKAGE__->table('users'); |
1107 | |
1108 | __PACKAGE__->add_columns(qw/user_id email password |
1109 | firstname lastname active |
1110 | admin/); |
1111 | |
1112 | __PACKAGE__->set_primary_key('user_id'); |
1113 | |
1114 | sub inflate_result { |
1115 | my $self = shift; |
1116 | my $ret = $self->next::method(@_); |
1117 | if( $ret->admin ) {### If this is an admin rebless for extra functions |
1118 | $self->ensure_class_loaded( $admin_class ); |
1119 | bless $ret, $admin_class; |
1120 | } |
1121 | return $ret; |
1122 | } |
1123 | |
1124 | sub hello { |
1125 | print "I am a regular user.\n"; |
1126 | return ; |
1127 | } |
1128 | |
1129 | |
1130 | package DB::Schema::User::Admin; |
1131 | |
1132 | use strict; |
1133 | use warnings; |
1134 | use base qw/DB::Schema::User/; |
1135 | |
1136 | sub hello |
1137 | { |
1138 | print "I am an admin.\n"; |
1139 | return; |
1140 | } |
1141 | |
1142 | sub do_admin_stuff |
1143 | { |
1144 | print "I am doing admin stuff\n"; |
1145 | return ; |
1146 | } |
1147 | |
1148 | B<Test File> test.pl |
1149 | |
1150 | use warnings; |
1151 | use strict; |
1152 | use DB::Schema; |
1153 | |
1154 | my $user_data = { email => 'someguy@place.com', |
1155 | password => 'pass1', |
1156 | admin => 0 }; |
1157 | |
1158 | my $admin_data = { email => 'someadmin@adminplace.com', |
1159 | password => 'pass2', |
1160 | admin => 1 }; |
1161 | |
1162 | my $schema = DB::Schema->connection('dbi:Pg:dbname=test'); |
1163 | |
1164 | $schema->resultset('User')->create( $user_data ); |
1165 | $schema->resultset('User')->create( $admin_data ); |
1166 | |
1167 | ### Now we search for them |
1168 | my $user = $schema->resultset('User')->single( $user_data ); |
1169 | my $admin = $schema->resultset('User')->single( $admin_data ); |
1170 | |
1171 | print ref $user, "\n"; |
1172 | print ref $admin, "\n"; |
1173 | |
1174 | print $user->password , "\n"; # pass1 |
1175 | print $admin->password , "\n";# pass2; inherited from User |
1176 | print $user->hello , "\n";# I am a regular user. |
1177 | print $admin->hello, "\n";# I am an admin. |
1178 | |
1179 | ### The statement below will NOT print |
1180 | print "I can do admin stuff\n" if $user->can('do_admin_stuff'); |
1181 | ### The statement below will print |
1182 | print "I can do admin stuff\n" if $admin->can('do_admin_stuff'); |
1183 | |
fe5cf259 |
1184 | =head2 Skip object creation for faster results |
1185 | |
1186 | DBIx::Class is not built for speed, it's built for convenience and |
1187 | ease of use, but sometimes you just need to get the data, and skip the |
137c657c |
1188 | fancy objects. |
1189 | |
1190 | To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>. |
1191 | |
1192 | my $rs = $schema->resultset('CD'); |
1193 | |
1194 | $rs->result_class('DBIx::Class::ResultClass::HashRefInflator'); |
1195 | |
1196 | my $hash_ref = $rs->find(1); |
1197 | |
1198 | Wasn't that easy? |
1199 | |
685dad64 |
1200 | =head2 Get raw data for blindingly fast results |
1201 | |
1202 | If the C<inflate_result> solution above is not fast enough for you, you |
1203 | can use a DBIx::Class to return values exactly as they come out of the |
1204 | data base with none of the convenience methods wrapped round them. |
1205 | |
1206 | This is used like so:- |
1207 | |
1208 | my $cursor = $rs->cursor |
1209 | while (my @vals = $cursor->next) { |
1210 | # use $val[0..n] here |
1211 | } |
1212 | |
1213 | You will need to map the array offsets to particular columns (you can |
1214 | use the I<select> attribute of C<search()> to force ordering). |
1215 | |
9e4c2514 |
1216 | =head2 Want to know if find_or_create found or created a row? |
1217 | |
1218 | Just use C<find_or_new> instead, then check C<in_storage>: |
fe5cf259 |
1219 | |
9e4c2514 |
1220 | my $obj = $rs->find_or_new({ blah => 'blarg' }); |
1221 | unless ($obj->in_storage) { |
1222 | $obj->insert; |
1223 | # do whatever else you wanted if it was a new row |
1224 | } |
1225 | |
7aaec96c |
1226 | =head3 Wrapping/overloading a column accessor |
1227 | |
1228 | Problem: Say you have a table "Camera" and want to associate a description |
1229 | with each camera. For most cameras, you'll be able to generate the description from |
1230 | the other columns. However, in a few special cases you may want to associate a |
1231 | custom description with a camera. |
1232 | |
1233 | Solution: |
1234 | |
1235 | In your database schema, define a description field in the "Camera" table that |
1236 | can contain text and null values. |
1237 | |
1238 | In DBIC, we'll overload the column accessor to provide a sane default if no |
1239 | custom description is defined. The accessor will either return or generate the |
1240 | description, depending on whether the field is null or not. |
1241 | |
1242 | First, in your "Camera" schema class, define the description field as follows: |
1243 | |
1244 | __PACKAGE__->add_columns(description => { accessor => '_description' }); |
1245 | |
1246 | Next, we'll define the accessor-wrapper subroutine: |
1247 | |
1248 | sub description { |
1249 | my $self = shift; |
1250 | |
1251 | # If there is an update to the column, we'll let the original accessor |
1252 | # deal with it. |
1253 | return $self->_description(@_) if @_; |
1254 | |
1255 | # Fetch the column value. |
1256 | my $description = $self->_description; |
1257 | |
1258 | # If there's something in the description field, then just return that. |
1259 | return $description if defined $description && length $descripton; |
1260 | |
1261 | # Otherwise, generate a description. |
1262 | return $self->generate_description; |
1263 | } |
1264 | |
40dbc108 |
1265 | =cut |